AbstractBoth methyl cis‐9‐octadecenoate and methyl trans‐9‐octadecenoate (commonly known as methyl oleate and methyl elaidate) were hydrogenated at operating conditions within the following ranges: 100–140°C, 1.7–14.6 at and 0.05–0.14% nickel catalyst. Correlations were developed for both geometrical and positional isomers as a function of iodine value. Decreases in pressure or increases in temperature resulted in a relatively greater increase in the amounts of positional isomers as compared to geometrical isomers. The rates of isomerization were found to vary between 0.7 to 2.5 times the rates of hydrogenation for hydrogenation runs with methyl cis‐9‐octadecenoate. The ratio between these two rates increased with higher temperatures or lower pressures. The rates of hydrogenation were compared for methyl cis‐9‐octadecenoate, methyl trans‐9‐octadecenoate, and cottonseed oil. Hydrogenation rate constants decreased in the following order: methyl trans‐9‐octadecenoate, methyl cis‐9‐octadecenoate, and cottonseed oil. The induction period that occurred only when a new catalyst was used depended on the temperature, pressure, and fatty feedstock being hydrogenated. The catalyst was activated to a considerable